1. Field of the Invention
This invention concerns dialysis equipment, namely a dialysis apparatus with a unit to produce a dialysis solution from a concentrate and water.
Dialysis equipment of the described kind is already known. It usually contains a conductivity cell as a detector mounted upstream of the dialyzer in order to measure the temperature-compensated conductivity value of the dialysis solution thereby to indicate a change in the electrolyte contents of the dialysis solution.
The detector itself serves not only to adjust the electrolyte contents of the dialysis solution, but also to switch off the entire device if the latter causes a critical condition in the patient. To regulate the electrolyte composition of the dialysis solution, the conductivity cell used as detector controls a pump which pumps the concentrate from a concentrate storage tank into the mixing unit. The mixing unit, on the other hand, is equipped with a tap water connection through which controlled water is supplied. In the mixing unit itself, water and concentrate are mixed and heated under control so that the desired composition of the dialysis solution is obtained at the outlet of said unit.
This dialysis solution is routed through the dialyzer, wherein the blood is cleared of urinary substances and fluid is withdrawn.
Because of the high exchange capacity of modern dialyzers, urinary substances are removed very rapidly from the blood and the dialysis time is thus reduced. Thus, in highly effective dialyzers, the treatment time can be reduced to 3.times.2 hours a week, within which not only the urinary substances such as urea but also excessive fluid are removed.
The withdrawal of the excess fluid demands a very precise control of the fluid balance, requiring that this process take place only with fluid-balancing devices. Despite precise balancing, the patients still experience some typical undesirable dialysis side effects such as headache, vomiting and muscle cramps designated as "disequilibrium syndrome." The reason is probably the excessively rapid withdrawal of sodium ions from the blood based on the difference of sodium concentration in the blood (extracorporal circulation) and in the dialysis solution. The higher the exchange capacity of the dialyzer, the lower may be the admissible gradient of sodium concentration between blood and dialyzing solution. Thus, a difference of a maximum of 10 nmol/1 sodium should be admissible for normal dialyzers, reduced to one half this value in high-performance dialyzers.
However, the sodium contents in the patient's blood differs and is commonly still outside of normal range of 135-147 nmol/1. In order to prevent the above-described dialysis symptoms, it is advisable to work with a sodium concentration of about 144 nmol/1 in the dialysis solution. The consequence is that the patient becomes thirsty during the treatment and accumulates relatively large amounts of liquid until the next dialysis treatment and is thus over-watered. It is not unusual to observe excess weight of up to 6 kgs. This added liquid must then be ultrafiltered during the treatment time of about 2-3 hours to withdraw the required quantity of sodium with this volume of liquid. In fact, however, this prior method of treatment is not sufficiently precise to entirely prevent the above symptoms during treatment.
Furthermore, the excessive over-watering which occurs between treatments is not at all good for the organ, yet it can hardly be avoided with the methods of the prior art.
2. Description of the Prior Art
Devices have already been developed (e.g., SERATRON of Cordis-Dow) which, based on a dialysis solution with predetermined composition, change the composition during the time of dialysis, said change taking place in accordance with a set program. The process is known as "sodium modelling." This program has, of course, the disadvantage that it is not at all tailored to individual requirements. Due to the fixed preprogrammed concentrations, difficulties will arise in patients with differing sodium levels. Besides, this program does not take into account the differences between the exchange capacity of the various dialyzers, so that even here disequilibrium symptoms cannot be avoided.
The prior art has been of the opinion that a determination of sodium elimination during dialysis would be impossible, since even at a very low measuring error of 1%, there could be over the duration of the dialysis a high absolute deviation, i.e., a sodium loss or increase. Accordingly, determination of sodium elimination in dialysis was abandoned (see H. G. Sieberth, et al., "Modern Problems of Dialysis Processes and Kidney Insufficiency," 3rd Symposium Innsbruck 1969, pp. 206-214, especially pg. 211, .sctn.3).
Due to such measuring difficulties, the prior art in general has operated with certain predetermined compositions of the dialysis solution which were either constant or variable in accordance with a certain program (sodium modelling). Consequently, to this date patients have necessarily been subjected to a determined composition of the dialysis solution instead of adapting the composition to the patient, since the latter was not believed possible.